| PDF: | |
| Time: | 2011 |
| Journal: | Chinese Journal of Geophysics |
| Volumn: | 54 |
| Issue: | 2 |
| Pages: | 524-533 |
| Type: | SCI |
| Author: | Yulong Huang,Deyou Sun,Pujun Wang,Licai Qu |
Abstract: | Flow units are the most elementary constituents of basaltic lava strata, and the zonation of pores and fractures determines the capability and distribution of basaltic reservoirs. Both outcrop and borehole information are used to build the geologic model of basaltic lava flow units, indicating that each unit is composed of three parts such as the upper vesicular zone, the central massive zone and the lower vesicular zone from top to bottom. Three electro-facies including alteration zone, vesicular zone and massive zone were identified by combining the natural gamma log (GR), acoustic log (DT), density log (RHOB), electrical resistivity (LLD) and neutron log (NPHI). Natural gamma-ray spectral logging (K, Th and U) were also utilized to distinguish intervals with abnormal high gamma values. Alteration zone is characterized as high in GR, DT and NPHI values while low in LLD and RHOB values, contrarily does the dense zone, and vesicular zone lies between. Logging response to the zonation of basaltic flow units indicates porosity, fracturing and alteration changes gradually and cyclically in the vertical profile. Alteration and vesicular zone are differentiated by K-GR cross-plots, and massive zone is further discriminated with them by DT-RHOB cross-plots. Eruption units are composed of single or several flow units, and with longer volcanic quiescence lies between, four types of boundaries with abnormal high GR values as a result of enriched K contents are distinguished including alteration and weathering zone, sedimentary and tuff interbeds. Moreover, the four boundaries is differentiated with Th-U and K-Th/U cross-plots depending on their different origins. |